Catch by the fingertip? (4)
I believe the answer is:
nail
I believe this is a double definition.
'catch' is the first definition.
(nail can mean to catch or arrest)
'fingertip?' is the second definition.
(I've seen this in another clue)
'by the' is the link.
(Other definitions for nail that I've seen before include "Small metal spike" , "Metal pin, hit it on the head" , "Fastening device" , "'For want of a . . . . the shoe was lost'" , "Horny part of the digit" .)